Di (orthoacylaminoaryl) disulfide softeners for rubbers



Patented May 24, 1949 DI (ORTHOACYLAMINOARYL) DISULFIDE SOFTENERS FORRUBBERS Philip T. Paul, Naugatuck, 001111., assignor to United StatesRubber Company, New York, N. Y., a corporation of New Jersey No Drawing.Application January 26, 1945, Serial No. 574,817

18 Claims. 1

This invention relates to softeners for rubbers, and more particularlyto the softening or plasticizing of natural rubbers, and syntheticrubbers, such as polymerized chloro-2-butadiene-1,3 commercially knownas neoprene or GRM rubber, copolymers of butadiene-1,3 and styrene,commercially known as Buna S or GRS rubber, and copolymers ofbutadiene-1,3 and acrylonitrile, commercially known as Buna N or GRNrubber.

I have discovered that di(orthoacylaminoaryl) disulfides are excellentsofteners for natural rubher, and for synthetic rubbers such as polymersof butadienes-l,3 and copolymers of butadienes- 1,3 with otherpolymerizable compounds which are capable of forming copolymers withbutadienes-1,3. The di(orthoacylaminoaryl) disulfides which are the newsofteners for various rubbers according to the present invention may bedesignated by the general formula H v n R-N (aromatlc)S-S-(aromatic) N-Rwhere R is an acyl radical, that is, a radical derived from an organicacid by removal of the hydroxyl group, and the nitrogens are in orthopositions to the sulfur atoms. radical R are formyl, acetyl, propionyl,butyryl, valeryl, caproyl, capryl, pelargonyl, myristyl, palmitoyl,stearoyl, margaryl, crotonyl, benzoyl,

- naphthoyl, p-phenyl benzoyl, mono-chloracetyl,

dichloracetyl, benzene sulfonyl, p-tolyl sulfonyl, thioacetyl,thiopropionyl. The aromatic nucleus of the general formula may be anarylene nucleus of the benzene, naphthalene, or biphenyl series whichmay be unsubstituted save for the sulfur and amino group or which may beotherwise substituted as by such groups as alkyl, aryl, hydroxyl,halogen, aryloxy, alkoxy, tertiary amino. The preferreddi(orthoacylaminoaryl) disulfides are the di(2-acylaminophenyl)disulfides, those in which the acyl radicals are derived from aromaticacids being di(2-aroyl'aminophenyl) disulfides and those in which theacyl groups are derived from alkanoic acids beingdi(2-alkanoylaminophenyl) disulfides. The softener 2,2-dithio bisacetanilide, otherwise known as 2,2'-diacetamino diphenyl disulfide,having the formula Examples of the acyl' dithio bis (4-methoxyacetanilide), 2,2'-dlthio bis (4 phenoxy acetanilide), 2,2'-dithio bis(4- chloro acetanilide), 2,2'-dithio bis (4-dimethylaminoacetanilide)2,2-dithio bis (l-acetyl amino naphthalene), 1,1'-dithio bis (2-acetylamino naphthalene) Di(orthoacylaminoaryl) disulfides are known per seand may be prepared in known manner by acylatin the di(orthoaminoaryl)disulfides. For example, 2,2'-bis thioaniline may be prepared fromaniline and sulfur according to the procedure of Hofman in Berichte derDeutschen Chemischen Gesellschaft, vol. 27, p. 2807 (1894). The 2,2 bisthioaniline may be acylated with glacial acetic acid and aceticanhydride according to the method of Clark, Journal of the ChemicalSociety (London), of 1928, page 2313, to give 2,2'-dithio bisacetanilide or 2,2-diacetamido diphenyl disulfide. Clark similarlydiscloses the preparation of 2,2'-dithio bis propionanilide from2,2'-bis thioaniline and propionic acid, and also 2,2'-dithio bisbenzanilide from 2,2-bis thianiline and benzoyl chloride. 2,2'-dithiobis formanilide may be prepared from 2,2'-bis thioaniline and formicacid by the method of Tomlinson, Journal of the Chemical Society(London) of 936, p. 1607. The amount of di(orthoacylaminoaryl) disulfideis not critical, generally amounts from about .5 part to'5 parts or moreper parts small amount of di(orthoacylaminoary1) disulfide' in a mixer,or on a mill at conventional milling temperature. Synthetic rubberswhich are polymers of butadienes-I,3 and copolymers of butadienes-1,3with other polymerizable compounds which are capable of formingcopolymers with butadienes-1,3 are-also readily plasticized by similarlyincorporating therein a di(orthoacylaminoaryl) disulfide. Such syntheticrubbers are known. Examples of synthetic rubbers which are polymers ofbutadie'nes-LS are polymerized butadiene-LS, methyl-2-butadiene-1,3(isoprene), chloro-2-butadiene-1,3 (chloroprene), piperylene,2,3-dimethylbutadiene-1,3. Illustrative of other polymerizable compoundswhich are capable of that is, a group which substantially increases theelectrical dissymmetry or polar character of the molecule. Examples ofcompounds which contain a cHF-o group and are copolymerizable withbutadienes 1,3 are aryl oleflns, such as styrene and vinyl naphthalene;the alpha methylene carboxylic acids, and their esters, nitriles, andamides such as acrylic acid, methyl acrylate, methyl methacrylate,acrylonitrile, methacrylonitrile, methacrylamide; isobutylene; methylvinyl ether; methyl vinyl ketone; vinylidene chloride. The expression arubber as used herein refers to such natural and artificial rubbers.Present day commercial synthetic rubbers of the above types arepolymerized chloro-2-butadiene-1,3, known as neoprene or GRM rubber,copolymers of butadiene-l,3 and styrene, known as Buna S or GRS rubber,and copolymers of butadiene-1,3 and acrylonitrile, known as Buna N orGRN rubber.

The following examples are illustrative of the softening or plasticizingeffect of di(orthoacy1 aminoaryl) disulfides on various rubbers,particularly on the commercial general purpose Buna S or GRS rubber, andother commercial rubbers. In the method of testing the effectiveness ofa di(orthoacylaminoaryl) disulfide on a rubber, equal parts of therubber itself were placed on the two halves of a divided mill having itsrolls heated to approximately 250 F. At this temperature, the rubberquickly smoothes out forming two separate continuous sheets around theroll. As soon as these continuous sheets have been formed, the chemicalto be tested is added to one of these sheets. The milling of both sheetsis continued for approximately ten minutes after which the two sheetsare removed from the mill and allowed to stand twelve to fourteen hoursat room. temperature. In some cases, a different milling time was used.In the examples below, it is to be understood that a ten minute millingperiod was used unless otherwise specified. After such restf-the twosamples, namely, the control sheet to which no di(orthoacylaminoaryl)disulfide had been added, and the sheet to which the chemical had beenadded, are tested in a Mooney shearing disc plastometer. This instrumenthas been described by M. Mooney in Industrial and Engineering Chemistry(Anal. ed.) 6, 147 (1934). By means of this device, the viscosity of aplastic material in shear may be readily and quantitatively measured.The readings recorded in the data in the following examples areviscosity readings after four minutes between platens of the instrumentat 212 F., a one minute warm up period being used. The'readings arebased on an arbitrary standard, the lower the readings, the lower theviscosity and hence :the greater the plasticity.

' ErampleI The following table of Mooney viscosi i s on various samplesof GRS rubber (commercial copolymer of butadiene-1,3 and styrene)containing various dl(orthoacylaminoary1) disulfides and thecorresponding control samples in each case illustrate the effectivenessof these chemicals as softeners for GRS rubber. the differences in theviscosities of the various controls show the great variations in thistyp of synthetic rubber.

Tests on GRS rubber with the unsubstituted diphenyl disulfide, and withacetanilide itself do not show the softening efiect of thedl(orthoacylaminoaryl) disulfides as illustrated in the above table. Forexample, Mooney viscosities of GRS rubber as a control and with 2 partsdiphenyl disulfide per 100 parts of the GRS rubber ran 58 and 76respectively; another control and sample with 2 parts acetanilide (22minute milling period) gave Mooney viscosities of 29 and 34respectively, showing a lack of softening effect of these chemicals ascompared with the di(orthoacylaminoaryl) disulfides as shown in theabove table.

Example II In the following table are shown Mooney viscosities onvarious control samples of commercial natural rubber, Hevea Braziliensissmoked sheet, and samples containing 2 parts of variousdi(orthoacylaminoaryl) disulfides per 100 parts of rubber.

Mooney viscosities on a smoked sheet control and the smoked sheet with 2parts diphenyl disulphide per 100 parts rubber ran 80 and 75respectively; another control and sample with 2 parts acetanilide gaveMooney viscosities of 80 and 81 respectively, showing a lack ofsoftening effect as compared with the chemicals in the table above.Another control and sample with 2 parts of 2,2-diamino diphenyldisulfide (2,2'- bis thioaniline) gave Mooney viscosities of 76 and 56respectively, showing the superiority as plasticizers for rubber of thedi(orthoacylaminoaryl) disulfides shown in the above table over the2,2-bis thioaniline without acylation. Another disadvantage of 2,2-bisthioaniline is its extreme toxicity.

Example III Tests similar to those of Examples I and II on polymerizedchloro-2-butadiene-L3 commercially known as neoprene or GRM rubber, with2 parts of various di(orthoacylaminoaryl) disul- Incidentally,

, 2.2'-Dithio bis parts of said rubber.

' fides as softeners per 100 parts of the GRM rubber gave results asshown in the following table:

Mooney Viscosity Di orthoa lamino l disulflde W 7 With cmml Chemical2,2'-Dithio bis acetanilide iod) Example IV Tests similar to those ofExamples I and II Mooney Viscosity Di(orthoacylaminoaryl) disuliideOontrol 2,2'-Ditliio bis acetanilide (20 minute milling period2,2'-Dithio his ropionanilide enzanilide Rubbers which may be mixed'withthe di (orthoacylaminoaryl) disulfides according to the presentinvention may be mixed with various other This is a continuation-in-partof application Serial No. 522,625, filed February 16, 1944, nowabandoned.

In view of the many changes and modifications that may be made withoutdeparting .from the principles underlying the invention, referencevshould be made to the appended claims for an understanding of the scopeof the protection afforded the invention.

' With Chemical 4. A composition of matter comprising a synthetic rubbercopolymer of butadiene-1,3 and styrene with which is admixed .5 to 5parts of per 100 parts di(orthoacylaminoaryl) disulflde per 100 parts ofsaid rubber. I

7. Acomposition of matter'comprising natural 7 rubber and, as a softenertherefor, 2,2'-dithio bis.

acetanilide. the said 2,2'-dithio bis acetanilide being present in aquantity not more than 5 parts per 100 parts of said rubber.

8. A composition of matter comprising polymerized chloro-2-butadiene-L3with which is admixed .5 to'5 parts of a di(orthoacylaminoaryl)vdisulflde per 100, parts of said polymer.

9. A composition of matter comprising polymerized chloro-2-butadiene-1,3and, as a softener therefor, 2,2'-dithio bis acetanilide, the said 2,2'-

Having thus described my invention, what I claim and desire to protectby Letters Patent is:

1. A composition of matter comprising a ,rubf ber selected from thegroup consisting of natural rubber, polymers of butadienes-1,3,- and copolymers of butadienes-1,3 with a compound which contains a CH2=C groupand is copolymerizable with butadienes-1,3, and, as a softener therefor,a di(orthoacylaminoaryl) disulfide, the said di(orthoacylaminoaryl)disulfidebeing present in a quantity not more than 5 parts per 100 partsof said rubber.

2. A composition of matter comprising a rub-' ber selected from thegroup consisting of natural rubber, polymers of butadienes-1,3, andcopolymers of butadienes-l,3 with a compound which contains a CH2=Cgroup and iscopolymerizable with butadienes'-l,3 and, as a softenertherefor, a di(2-alkanoy1aminophenyl) disulfide, the saiddi(2-alkanoylaminophenyl) disulfide being 'present in aquantity not morethan 5 parts per 100 3. A composition of matter comprising a rubberselected from the group consisting of natural rubber, polymers ofbutadienes-1,3, and copolymers of butadienes-1,3 with a compound whichcontains a CH2=C group and is copolymerizable with butadienes-1,3, withwhich is admixed .5 to 5 parts of 2,2'-dithio bis acetanilide' per 100parts of said rubber.

' mers of butadienes -1,3, and copolymers of bu- 5 dithio bisacetanilide being present in a quantity not more than 5 parts per partsof said polymer..

10. The method of plasticizing a rubber selected 7 from the groupconsisting of natural rulme'r, polymers of butadienes-1,3, andcopolymers of butadicues-1,3 with a compound which contains a 1,3, whichcomprises incorporating therein .5 to 5 partsof a di(orthoacylaminoaryl)disulfide per 100 parts of said rubber.

11. The method of plasticizing a rubber selected from the groupconsisting of natural rubber, polymers of butadiene's-L3, and copolymersof butadienes-1,3 with a compound which contains a CH2=C group and iscopolymerizable with butadienes-1,3,,which comprises incorporatingtherein .5 to 5 parts of a di(2-acylami nophenyl) disulfide per 100parts of said rubber-to soften the same. z

12." The method of plasticizing a rubber selected from the groupconsisting of natural rubber, polytadienes-1,3',with a compound whichcontains a CH=C group and is copolymerizable with butadienes 1,3, whichcomprises f incorporating therein .5 to 5 parts of 2,2'-dithio bisacetanilide, per 100 parts of said rubber to soften the same.

13. The method of plasticizing a synthetic rubber copolymer ofbutadiene-l,3 and styrene which comprises incorporating therein a,di(0rthoacylaminoaryl) disulfide, the said di(orthoacylaminoaryl)disulfide being in a quantity not more than I 5 parts per 100 parts ofsaid copolymer.

14. The method of plasticizing a synthetic rubber copolymer ofbutadiene-IB and styrene which comprises incorporating therein .5 to 5parts of 2,2'-dithio bis acetanilide therein per 100 parts of saidcopolymer.

15. The methodof 'plasticizingnatural rubber which comprisesincorporating therein a di(orthoacylaminoaryl) disulfide, the saiddi(orthoacylaminoaryl) dis"ulflde being in a quantity not more than 5parts per 100 parts of said rubber.

16. The method of plasticizing natural rubber which comprisesincorporating therein .5 to 5 parts of 2,2'-dithio bis acetanilide per100 parts of said rubber.

1'1. The method of plasticizing polymerized 10 Number rating therein ..5to 5 ports of 2,2"-dithio his acetanilide therein per 100 partsot'saidpolymer.

PmmP'nPAoL.

REFERENCES CITED:

The following references are of record in the file of this patent:

FOREIGN PATENTS Country Date 542,645 Great Britain Jan. 21, 1am

